Optical measurement method and device

ABSTRACT

An optical measurement of a crystalline sample to be measured. The sample is irradiated with an exciting light from the polarization direction in which the Raman scattering is prohibited by the selection rule. When a metal probe is brought to proximity to the sample to be measured, the selection rule is eased locally only in the proximity portion near the probe end in order that Raman scattering becomes active. Thus, a Raman signal only from the proximity portion near the probe end is detected. An optical measurement apparatus having an optical arrangement for measuring a signal light re-emitted from a sample to be measured when the sample is irradiated with an exciting light is provided. The optical measurement apparatus comprises a means for limiting the polarization state of the exciting light or signal light and a means for bringing a metal probe near the sample to be measured. The optical measurement apparatus is used to measure the signal light obtained by locally easing the limitation on the polarization state by bringing the metal probe near the sample. Therefore, Raman scattering light from silicon or the like can be measured with high space-resolution exceeding the light diffraction limit.

TECHNICAL FIELD

This invention relates to a method of measuring optical characteristicsand, particularly, Raman spectra of a sample with a spatial resolutionhigher than the resolution of ordinary optical microscopes and to adevice for implementing the method.

BACKGROUND ART

In recent years, study has been vigorously forwarded in the fields ofnano-structures and nano-devices, and a spectrophotometric technologyfeaturing a high resolution has been desired for evaluating propertiesof a variety of samples in these fields. In the silicon devices, forexample, strain in Si seriously affects the device characteristics suchas mobility and the like. Therefore, it is very important to knowspatial distribution of the strain in Si device with a high resolution.One of the strain measurement methods is based on the Raman measurement.The Raman measurement is based on a principle that a peak position of aRaman signal shifts depending upon the strain. Upon mapping peakpositions of Raman signals, therefore, it is allowed to know thedistribution of strain.

The optical measurement with a high spatial resolution has heretoforebeen conducted by using a microscope. However, the above microscopicoptical measurement encounters a barrier of diffraction limit whichmakes it difficult to accomplish the space resolution of finer than onemicron. In modern silicon devices, the structural sizes are reaching theorders of submicrons and nanometers, and a measuring method of a higherresolution is desired. In recent years, therefore, various attempts havebeen made for improving the spatial resolution relying upon thenear-field spectrophotometry by using a probe such as an optical fiber.

This method uses a near-field light leaking from a very small apertureat the end of the probe. Therefore, when it is attempted to observemaintaining a resolution of finer than 100 nm, the aperture size, too,must be decreased to be smaller than 100 nm, resulting in a very greatloss of light quantity and arousing such a serious difficulty in themeasurement that the method can be applied to only those samples thatproduce large signals. In the case of the Raman measurement of silicon,in particular, the optical fiber itself contains silicon which is acause of disturbing the emission of Raman signals making it furtherdifficult to take a measurement.

To solve this difficulty, one of the technologies proposed in the fieldof Raman spectroscopy uses a metallic AFM (atomic force microscope)probe. According to this method, Raman signals are enhanced only nearthe end of the probe due to a local electric field at an end of themetal probe, enhancing the space resolution. In this method, a largeenhancing effect is obtained when two metals are brought close to eachother maintaining a very small gap and when a sample to be measured isplaced in the gap. Therefore, though the result can be obtained to someextent in the measurement of molecules and ultra-fine particles, themethod cannot still be applied to the measurement of solid materials.This is because the sample to be measured which is a solid materialcannot be placed between the two metals described above. Besides, strongsignals in the far visual field are excited at positions away from themetal probe and conceal the signals in the near field.

The following patent document 1 discloses technology which uses atransmission type electron microscope to detect fine crystallinedistortion in semiconductors. The image obtained by the transmissiontype electron microscope can be converted into a digital image, and thepattern can be calculated by two-dimensional Fourier transform.

[Patent document 1] JP-A-2000-65762

DISCLOSURE OF THE INVENTION

It is an object of this invention to solve the problem that in thenear-field optical measurement, it is very difficult to detect very weaklight such as of the Raman measurement.

According to the present invention, a method for solving the aboveproblem is found by a technique that will be described below. That is,an exiting light is caused to fall on a single crystalline substratesample such that a polarization direction thereof is prohibited by theselection rule. In the Raman scattering, for example, if the exitinglight is caused to fall on the (001) plane of single crystalline siliconsuch that the polarization direction thereof is in the [100] directionso as to detect the scattered light that is polarized in the [100]direction only, the first-order Raman scattered light appearing near awave number 520 cm⁻¹ is prohibited by the selection rule. This methoduses strict selection rules for the first-order Raman scattering ofcrystalline Si.

In the Raman scattering, similarly, if the exciting light is incident onthe (001) plane of single crystalline silicon and polarized in the [100]direction so as to detect the scattered light that is polarized in the[100] direction only, the first-order Raman band of Si at 520 cm⁻¹ isforbidden by the selection rule. Further, if the exciting light isincident on the (001) plane of single crystalline silicon from thedirection perpendicular to the plane and polarized in the [110]direction so as to detect the scattered light that is polarized in adirection at right angles therewith only, the first-order Raman band ofSi at 520 cm⁻¹ is forbidden by the selection rule. For the (110) plane,further, for both the incident and scattered lights polarized parallelto the [001] direction the Raman band at 520 cm⁻¹ is forbidden.

Here, if a metallic probe is brought close to the irradiated portion,the polarization of the local electric field near the tip will differfrom the polarization of the incident light whereby the Raman scatteringbecomes active and its intensity is enhanced by an electric field of asurface plasmon induced at the end of the probe. Signals from portionsaway from the probe are forbidden and are very weak. However, the Ramanscattering is permitted on a portion close to the probe. Therefore, thesignals near the end of the probe can be separated and taken out. Thatis, the Raman signals from only the portion near the end of the probecan be detected to realize a high resolution. The resolving powerdepends on the diameter of the probe tip. The resolving power of theorder of nanometers can be obtained if the diameter of the tip of theprobe is sufficiently decreased.

Further, if just the end of a probe is made of a material having highscattering efficiency for the exciting light but the other portions ofthe probe being made of a material having low scattering efficiency, theincident light is scattered mainly by the end of the probe. For thescattered light, the polarization direction rotates from the basicexciting light and, besides, the traveling direction of light changes,whereby the selection rule is relaxed, the Raman scattering is activatedand the intensity is enhanced by an electric field of surface plasmoninduced at the end of the probe. Signals from portions away from theprobe are forbidden and are very weak. However, if the probe is broughtsufficiently close to the sample, the range where the scattered lightreaches from the end of the probe is limited to the vicinity of theprobe, and the Raman scattering is permitted at that portion. Therefore,the signals near the end of the probe can be separated and taken out. Itis effective to use short wavelength light, i.e., an ultraviolet ray asthe exciting light to increase the absorption coefficient of the sampleand to decrease the penetration depth of the scattered light into thesample. Employment of this configuration makes it possible to detectRaman signals from only a portion near the end of the probe to realize ahigh spatial resolution. The resolution depends on the diameter of fineparticles carried at the end of the probe. The resolution of the orderof nanometers can be obtained if the diameter of the fine particles issufficiently small.

A manner in which the selection rule is relaxed by the probe can beproved by the theoretic calculation. FIG. 1 shows the calculated resultsfor the cases where light of a wavelength of 400 nm falls onto the endof a silver probe of a spheroid shape and where the polarizationdirections and intensities of near-field are calculated for differentpolarization directions of incident light (arrow at an upper part of theellipse in each drawing): (a) polarization of the incident light isparallel to, (b) perpendicular to, and (c) tilted by 45 degrees withrespect to the rotary axis (long axis) of the probe. The polarizationdirection and intensity of the near-field light are expressed by thedirection and length of the arrow on the line at the top of the ellipsein the drawings. It is shown that when the polarization of incidentlight is parallel to the long axis, a strong near-field light parallelwith the direction of incident polarization is induced. When thepolarization of incident light is perpendicular to the long axis, a weaknear-field light with the polarization parallel to that of the incidentlight is induced. When the polarization of incident light is tilted by45 degrees, a strong near-field light is induced in the direction thatis not parallel to the direction of the incident polarization.

Therefore, even when the incident light has a polarization direction inwhich the Raman scattering is prohibited, the induced near-field lightpossesses the Raman-active polarization direction if the angle betweenthe polarization direction and the axis of the probe is set to be, forexample, 45 degrees as described above, and there can be observed Ramanscattered signals induced by the near-field light only. In a practicaldevice, the end of the probe is not a perfect spheroid but has some fineruggedness. Therefore, even without correct control of the polarizationdirection of incident light in respect to the probe axis, a near fieldis induced in a polarization direction different from the incidentpolarization direction. Namely, the Raman selection rule can be relaxedeven by simply bringing the probe close to the sample.

This invention solves the above problems in a manner as described above.More concretely, the invention solves the problems by a method and adevice as described below. Namely, an optical measurement method of theinvention includes an optical arrangement for measuring a signal lightfrom a sample to be measured by irradiating the sample with excitinglight, wherein the optical arrangement is the one that prohibits thesignal light by a selection rule, and a probe is brought close to thesample to be measured to locally relax the selection rule in only aportion near the end of the probe thereby to obtain the signal light.

Another optical measurement method of the invention includes an opticalarrangement for measuring a signal light from a sample to be measured byirradiating the sample with exciting light, wherein the opticalarrangement is the one that prohibits the signal light by a selectionrule, and a probe having an end portion and other portions made ofdifferent materials at least on the surfaces thereof is brought close tothe sample to be measured to measure the signal light.

A further optical measurement method of the invention is concerned withthe above optical measurement method, wherein the end portion has amaterial in the surface thereof different from the other portions due tothe surface treatment.

A further optical measurement method of the invention is concerned withthe above optical measurement method, wherein the end portion is made ofa material different from that of the other portions.

A further optical measurement method of the invention is concerned withthe above optical measurement method, wherein the probe uses, in the endportion thereof, a material having a large efficiency for scattering theexciting light and uses, in other portions thereof, a material having asmall efficiency for scattering the exciting light.

A further optical measurement method of the invention is concerned withthe above optical measurement method, wherein the probe carries, on theend portion thereof, fine particles of a material different from that ofthe other portions.

A further optical measurement method of the invention is concerned withthe above optical measurement method, wherein the other portions aremade of a material transparent for the excitation light.

A further optical measurement method of the invention is concerned withthe above optical measurement method, wherein the other portions aremade of a glass or a plastic material.

A further optical measurement method of the invention is concerned withthe above optical measurement method, wherein the fine particles arefine metal particles.

A further optical measurement method of the invention is concerned withthe above optical measurement method, wherein the metal is any one ofsilver, gold, platinum or copper.

A further optical measurement method of the invention is concerned withthe above optical measurement method, wherein the end portion and thevicinity thereof are immersed in a solution having a refractive indexclose to a refractive index of a material of the other portions, and ameasurement is taken by decreasing the scattering of the exciting lightin the portions other than the end portion of the probe.

A further optical measurement method of the invention is concerned withthe above optical measurement method, wherein the exciting light isultraviolet light.

A still further optical measurement method of the invention causesexciting light to fall on a crystalline sample to be measured from apolarization direction in which the Raman scattering is prohibited bythe selection rule, and brings a probe close to the sample to bemeasured to locally relax the selection rule in only a portion near theend of the probe thereby to activate the Raman scattering and to obtainRaman signals from only the portion near the end of the probe.

A further optical measurement method of the invention is concerned withthe above optical measurement method, wherein the sample to be measuredis a flat plate of a (001) orientation having a crystal structure whichis a diamond structure or a zinc-blende structure, and scattered lightof [100] polarization is detected with the exciting light beingpolarized in the [100] direction.

A further optical measurement method of the invention is concerned withthe above optical measurement method, wherein the sample to be measuredis a flat plate of a (001) orientation having a crystal structure whichis a diamond structure or a zinc-blende structure, the exciting light isincident on the sample in a direction [00-1] and is polarized in adirection [100] or [010], and signal light scattered in a direction[001] which is the same polarization direction as the exciting light isdetected.

A further optical measurement method of the invention is concerned withthe above optical measurement method, wherein the sample to be measuredis a flat plate of a (001) orientation having a crystal structure whichis a diamond structure or a zinc-blende structure, the exciting light isincident on the sample in a direction [00-1] and is polarized in adirection [110] or [1-10], and signal light scattered in a direction[001] which is a polarization direction at right angles with theexciting light is detected.

An yet further optical measurement method of the invention is concernedwith the above optical measurement method, wherein exciting light iscaused to fall on a (001) plane of single crystalline silicon from adirection perpendicular to the plane such that the exciting light ispolarized in the [110] direction and scattered light polarized in adirection at right angles therewith only is detected, or exciting lightpolarized in parallel with the [001] direction is caused to fall on the(110) plane to prohibit the Raman scattering polarized in parallel withthe [001] direction.

A further optical measurement method of the invention is concerned withthe above optical measurement method, wherein the probe is scanned tomeasure a spatial distribution of Raman signals.

A further optical measurement method of the invention is concerned withthe above optical measurement method, wherein the probe is the onecoated with silver or gold.

A further optical measurement method of the invention is concerned withthe above optical measurement method, wherein the sample to be measuredis any one of silicon, diamond, germanium, Si—Ge mixed crystal, ZnS,ZnO, BN, BP, AlP, GaN, GaP, GaAs, InP, InAs, MSe (M=Be, Cd, Hg, Zn, Mn)or a mixed crystal thereof.

Further, an optical measurement device equipment of the inventionincludes an optical arrangement for measuring a signal light from asample to be measured by irradiating the sample to be measured withexciting light, comprising means for limiting the polarized state of theexciting light or the signal light, and means for bringing a probe closeto the sample to be measured, wherein the probe is brought close to thesample to be measured to measure the signal light.

Another optical measurement device of the invention is concerned withthe above optical measurement device, wherein the probe has an endportion and other portions made of different materials at least on thesurfaces thereof.

A further optical measurement device of the invention is concerned withthe above optical measurement device, wherein the end portion has amaterial in the surface thereof different from the other portions due tothe surface treatment.

A further optical measurement device of the invention is concerned withthe above optical measurement device, wherein the end portion is made ofa material different from that of the other portions.

A further optical measurement device of the invention is concerned withthe above optical measurement device, wherein the probe uses, in the endportion thereof, a material having a large efficiency for scattering theexciting light and uses, in other portions thereof, a material having asmall efficiency for scattering the exciting light.

A further optical measurement device of the invention is concerned withthe above optical measurement device, wherein the probe carries, on theend portion thereof, fine particles of a material different from that ofthe other portions.

A further optical measurement device of the invention is concerned withthe above optical measurement device, wherein the other portions aremade of a material transparent for the exciting light that isirradiated.

A further optical measurement device of the invention is concerned withthe above optical measurement device, wherein the other portions aremade of a glass or a plastic material.

A further optical measurement device of the invention is concerned withthe above optical measurement device, wherein the fine particles arefine metal particles.

A further optical measurement device of the invention is concerned withthe above optical measurement device, wherein the metal is any one ofsilver, gold, platinum or copper.

A further optical measurement device of the invention is concerned withthe above optical measurement device, wherein the end portion and thevicinity thereof are immersed in a solution having a refractive indexclose to a refractive index of a material of the other portions, and ameasurement is taken by decreasing the scattering of the exciting lightin the portions other than the end portion of the probe.

A further optical measurement device of the invention is concerned withthe above optical measurement device, wherein the exciting light isultraviolet light.

A further optical measurement device of the invention is concerned withthe above optical measurement device, wherein the sample to be measuredis a flat plate of a (001) orientation having a crystal structure whichis a diamond structure or a zinc blende structure, and scattered lightof [100] polarization is detected with the exciting light beingpolarized in the [100] direction.

A further optical measurement device of the invention is concerned withthe above optical measurement device, wherein the sample to be measuredis a flat plate of a (001) orientation having a crystal structure whichis a diamond structure or a zinc blende structure, the exciting light isincident on the sample in a direction [00-1] and is polarized in adirection [100] or [010], and signal light scattered in a direction[001] which is the same polarization direction as the exciting light isdetected.

A further optical measurement device of the invention is concerned withthe above optical measurement device, wherein the sample to be measuredis a flat plate of a (001) orientation having a crystal structure whichis a diamond structure or a zinc blende structure, the exciting light isincident on the sample in a direction [00-1] and is polarized in adirection [110] or [1-10], and signal light scattered in a direction[001] which is a polarization direction at right angles with theexciting light is detected.

A further optical measurement device of the invention is concerned withthe above optical measurement device, wherein the probe is scanned tomeasure a spatial distribution of Raman signals.

A further optical measurement device of the invention is concerned withthe above optical measurement device, wherein the probe is the onecoated with silver or gold.

A further optical measurement device of the invention is concerned withthe above optical measurement device, wherein the sample to be measuredis any one of silicon, diamond, germanium, Si—Ge mixed crystal, ZnS,ZnO, BN, BP, AlP, GaN, GaP, GaAs, InP, InAs, MSe (M=Be, Cd, Hg, Zn, Mn)or a mixed crystal thereof.

A further optical measurement device of the invention is concerned withthe above optical measurement device, wherein provision is made of meansfor varying a distance between the probe and the surface of the sampleto be measured, and means for taking a difference between the intensityof signal light of when the probe is brought close to the surface of thesample to be measured and the intensity of signal light when the probeis separated away therefrom.

A further optical measurement device of the invention is concerned withthe above optical measurement device, wherein provision is made of meansfor causing the exciting light to fall on the surface of the sample tobe measured nearly perpendicularly thereto and for detecting the signallight from the surface of the sample nearly perpendicularly thereto.

A further optical measurement device of the invention is concerned withthe above optical measurement device, wherein provision is made of meansfor bringing the probe close to the surface of the sample to be measuredfrom a tilted direction.

Being constituted as described above, this invention solves the problemthat in the near-field optical measurement, it is very difficult todetect very weak light such as Raman measurement and, particularly,solves the problem that in the near-field optical measurement by using ametal probe, the far field signals conceal signals in the near field todeteriorate the spatial resolution of measurement, and makes it possibleto measure the Raman scattered light from silicon which could not beaccomplished so far maintaining spatial resolution higher than thediffraction limit of light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the calculated results for the cases wherelight of a wavelength of 400 nm is caused to fall on the end of a silverprobe of a spheroid shape and where the polarization directions andintensities of near-field light induced by the interaction of light andprobe are calculated when the polarization direction of incident lightis (a) in parallel with, (b) perpendicular to, and (c) tilted by 45degrees with respect to, the direction of the rotation axis (long axis)of the probe;

FIG. 2 is a diagram schematically illustrating the arrangement foroptical measurement according to the invention;

FIG. 3 is a graph illustrating Raman spectra measured without a probe(lower graph); with a probe retracted away from the surface of thesample (middle graph), and with the probe is in contact with the surfaceof the sample (upper graph) in the forbidden polarization configuration(Si (001) surface; polarizations of the incident and scattered lightsare parallel to the [100] axis).

FIG. 4(a) is a graph illustrating the structure of the SOI island withthe strained Si film on the top and a change in the Raman spectra nearthe edge of the island (a), and (b) is a graph illustrating dependenceof the Raman shift of Si substrate, Si_(1-x)Ge_(x) and strained Si vs.the distance from the edge of the island;

FIG. 5 is a graph illustrating the results of measuring the reflectionspectra by arranging silver particles of a diameter of 50 nm and adiameter of 40 nm on an Si substrate;

FIG. 6 is a graph illustrating Raman spectra of Si by using an Sisubstrate on which silver particles of a diameter of 50 nm are arrangedat exciting wavelengths of 514.5 nm, 632.8 nm and 782 nm depending on aportion where the silver particles are existing and a portion where thesilver particles are not existing (attention should be given todifferent scales of the ordinate);

FIG. 7 is a graph drawn by plotting Raman signal intensities at 520 cm⁻¹according to the method of the patent while scanning the Si substrate onwhich silver particles of 50 nm diameter are arranged with a spacing of230 nm by using an AFM probe coated with silver in contact therewith;

FIG. 8 is a view schematically illustrating an arrangement for opticalmeasurement by using a probe on which silver particles are carriedaccording to the Example of the invention mentioned below, wherein theprincipal configuration is the one used in the above embodiment;

FIG. 9 is a graph illustrating the experimental results of the aboveExample and shows Raman spectra of Si with and without AFM probe for the364 nm excitation and forbidden polarization configuration (incidentlight is polarized parallel to the [110] axis of Si but the scatteredlight is polarized parallel to the [1-10] axis;

FIG. 10 is a diagram illustrating a sample structure used in a furtherExample of the invention;

FIG. 11 is a graph illustrating the results of measurement by using theabove sample, wherein (a) corresponds to the measurement without AFMprobe and (b) corresponds to the measurement with the Ag-particle-toppedAFM probe;

FIG. 12 is a view schematically illustrating a sample of when holes of adiameter of about 100 nm are etched in a silicon substrate and wheninner walls of the holes are thermally oxidized, wherein (a) is aperspective view and (b) is a sectional view along the portion A-A in(a); and

FIG. 13 is a graph illustrating dependence of the Raman shift on theprobe position for (a) Ag-particle-topped AFM probe (364 nm excitation)and (b) Ag-coated AFM probe (514.5 nm excitation).

BEST MODE FOR CARRYING OUT THE INVENTION

According to this invention, Raman signal from silicon can be measuredwith a spatial resolution better than the light diffraction limit by anoptical measurement method which includes an optical arrangement formeasuring a signal light from a sample to be measured by irradiating thesample with exciting light, wherein the optical configurations are theones that prohibit the signal light by the selection rule, and a probehaving an end portion and other portions made of different materials isbrought close to the sample to be measured to measure the signal light,by using an optical measurement device which includes an opticalconfiguration for measuring a signal light from a sample to be measuredby irradiating the sample with exciting light, comprising means forlimiting the polarization of the exciting light or the signal light, andmeans for bringing a probe close to the sample to be measured, the probehaving an end portion and other portions made of different materials andbeing brought close to the sample to be measured to measure the signallight.

EXAMPLE 1

FIG. 2 is a diagram schematically illustrating the arrangement formeasurement. The AFM probe coated with silver is mounted on a piezoelement and can be vibrated up and down by signals from a controller.Further, a piezo element is mounted on a stage on which a sample holderis mounted, and can be driven up and down and right and left by signalsfrom the controller. The exciting laser beam is focused on the surfaceof a sample by an objective lens, and the AFM probe coated with silveris brought close to the focusing portion. The operation of the AFM probeis controlled by the light from a laser diode and by a detector. Asshown, the laser beam for excitation is caused to so fall as to bepolarized in [100]. Of the scattered light collected by the objectivelens, the scattered light polarized in [100] only is guided to aspectrometer and is separated.

More concretely, the laser beam of 514.5 nm or 632.8 nm is caused tofall on a (001) substrate of Si perpendicularly thereto in a manner thatthe polarization direction is the [100] direction, is focused by theobjective lens into 1 to 2 μm on the surface of the sample, and the AFMprobe coated with silver and having an end of a diameter of 100 nm isplaced thereon. The arrangement of measurement is such that thescattered light is focused by the objective lens and is guided to thespectrometer.

FIG. 3 illustrates Raman spectra in comparison when the metal probe inthis arrangement is separated away from the surface of the sample byabout 500 nm and when the metal probe is brought close to the surface ofthe sample. That is, there are shown a Raman spectrum (lower graph)measured without an AFM probe, a spectrum (intermediate graph) of whenthe silver probe is separated away from the surface of the sample byabout 500 nm and a spectrum (upper graph) of when the silver probe is incontact in the forbidden arrangement on the Si (001) surface. Withoutthe metal probe, the peak is almost suppressed at the wavenumber of 520cm⁻¹. When the metal probe is brought into contact, however, the peak isobserved at 520 cm⁻¹. The peak appears because the selection rule islocally broken at the end of the probe and, hence, the signal is fromthe sample near the end of the probe. When the probe is separated awayby 500 nm, too, there appears a peak though it is considerably weakerthan that of when the probe is brought in contact. This is due to thefact that when the exciting light hits the metal probe, the polarizationdirection is affected not only by the near-field light but also slightlyby the light of far field. To obtain the effect of the near-field lightonly, therefore, a difference should be detected between the intensityof signal light of when the metal probe is brought close to the surfaceof the sample and the intensity of signal of when it is separated awaythereby to take out only those signals due to the near field and,accordingly, to improve the spatial resolution and the S/N ratio. TheS/N ratio of differential signal can be improved by using, for example,a piezo element, the sample being vibrated up and down at 10 Hzmaintaining an amplitude of 500 nm. Synchronized with the probemovement, the CCD sends data to a computer, and the differential signalis accumulated 100 times to improve the S/N ratio by 10 folds.

EXAMPLE 2

The following measurement is conducted to prove a high spatialresolution of the measurement method of this Example. Referring to FIG.4(a), the sample is a 5 μm wide island of a strained SOI(silicon-on-insulator) thin film formed by epitaxially growing Si in athickness of 14 nm on the (001) surface of SiGe (Ge composition of 28%)of a thickness of 40 nm. Here, a laser beam of 514.5 nm is caused tofall in a manner that the polarization direction thereof is in parallelwith [100]. The scattered light of which the polarization direction isin parallel with [100] only is detected by using a polarizer. FIG. 4(a)illustrates changes in the Raman spectra near the edge of the SOIisland, and (b) illustrates changes in the Raman shift.

Strained Si and Si have different lattice constants, therefore the peakposition of the Raman spectra shifts from ordinary 520 cm⁻¹ to ˜515cm⁻¹. The probe is scanning from the edge of the island to its interiorregion while monitoring the peak of 515 cm⁻¹. At the edge of thepattern, the Raman peak is centered at ˜516 cm⁻³, which, however,becomes ˜515 cm⁻¹ toward the interior region. The spatial resolution isabout 100 nm.

EXAMPLE 3

The measurement is taken in the same manner as in Example 2 but using atip having diameter of 50 nm. The spatial resolution is about 50 nm.

EXAMPLE 4

Silver particles of a diameter of 50 nm and of a diameter of 40 nm arearranged on an Si substrate, and reflection spectra are measured toobtain results as shown in FIG. 5. A peak near 600 nm in the reflectionspectrum of silver particles of 50 nm is caused by the excitation ofplasmon, and the polarization direction of scattered light changes. Withsilver particles of 40 nm, on the other hand, the above peak is notobserved and the polarization direction is preserved.

In this arrangement, the exciting light of a wavelength of 632.8 nm iscaused to fall such that the polarization direction of the excitinglight is in the [100] direction, and the Raman spectrum is measured inthe arrangement for detecting the scattered light polarized in the [100]direction only (forbidden configuration for the Raman peak of 520 cm⁻¹).The enhancement effect is obtained only for those silver particleshaving a diameter of 50 nm. This is due to that the polarizationdirection of the exciting light changes due to the silver particles of50 nm and the selection rule is relaxed.

FIG. 6 shows Raman spectra of Si (forbidden polarization configuration)for Si with and without 50 nm particles for the 514.5 nm, 632.8 nm and782 nm excitation wavelengths. In accordance with the plasmon resonanceposition, enhancement of the 520 cm⁻¹ band due to the depolarizationeffect is observed for the 514.5 nm and 632.8 nm excitations but is notfor the 782 nm excitation. As will be understood from the reflectionspectra of FIG. 5, this is due to the fact that the interaction betweenthe exciting light and the silver particles is small at the wavelengthsof 514.5 nm and 782 nm, and the polarization direction does not change.The second-order Raman band of Si centered at ˜950 cm⁻¹ is allowed forthe used polarization configuration and its intensity is not affected bythe presence of the Ag particles. This band can be used as a referencefor the 520 cm⁻¹ band intensity.

The above results are obtained for the silver particles on the Sisubstrate. This, however, can also be applied to a metal probe. Theprobe will produce better near field and better depolarization effectfor the wavelengths corresponding to its surface plasmon resonance. Thatis, by measuring the reflectivity, the wavelength can be found at whichthe exciting light and the metal probe interacts each other, and awavelength of exciting light suited for the measurement can beestimated. Further, the effect of the metal probe on the polarization oflight of far field described in Example 1 can be suppressed by selectingthe exciting wavelength.

Next, Raman intensities at 520 cm⁻¹ (forbidden polarizationconfiguration) were measured while scanning the Si substrate with ˜50 nmsilver particles arranged in a square lattice with ˜230 nm period byusing an AFM probe coated with silver in the contact mode (FIG. 7). Theexciting wavelength is 782 nm. This exciting wavelength is selectedsince the silver-coated AFM probe displays surface plasmon resonance at782 nm due to the prolonged shape of the probe but the silver particlesdoes not as obtained from the above experimental result (FIG. 5).

Referring to a graph of FIG. 7, when the AFM probe comes on a silverparticle, the near field by the AFM probe does not reach the surface ofSi and the Raman signal is not enhanced. When the AFM probe is not onthe silver particle, however, the Raman signal is enhanced due to theAFM probe near field. The graph tells that the spatial resolution is 100nm or better.

EXAMPLE 5

FIG. 8 illustrates a further Example of the invention. The probe havinga tip made of a material different from that of the other portions ofthe probe is brought close to the sample and locally depolarizes theincident light and relaxes the selection rules. Then, an allowed localRaman signal from the area near the end of the probe appears. In theExample of FIG. 8, the end of the probe is made of a different materialon at least the surface thereof by carrying fine metal particles such asof silver, gold, platinum, copper or the like.

FIG. 8 is a diagram illustrating the arrangement for measurement. Inthis diagram of the arrangement for measurement, the contents of theabove Examples 1 to 4 can similarly be applied except the pointconcerning the end of the probe and the vicinity thereof. In FIG. 8, theexciting laser beam is focused on the surface of a sample by anobjective lens, and a quartz probe carrying silver particles of adiameter of about 50 nm at the end thereof, which is purchased fromNanonics Co., is brought close thereto. The operation of the probe iscontrolled by the light from a laser diode and by a detector. As shownin an enlarged inset in the drawing, the incident laser light ispolarized in the [110] direction on the sample plane, and the scatteredlight is collected by the objective lens and only the componentpolarized perpendicular to the incident one is guided to a spectrometer.The exciting light is ultraviolet.

The laser beam of a wavelength of 364 nm polarized in the [110]direction is caused to fall normally onto a (001) substrate of Si. Thelaser beam is focused by the objective lens into a 1 μm spot on thesurface of the sample, and the quartz probe carrying on its tip a silverparticle of a diameter of about 50 nm is placed into the spot. Further,a glycerol liquid is dripped onto the surface of the sample so that theend part of the probe to be irradiated with the exciting light isimmersed therein. Glycerol prevents scattering of the light by the otherportions of the probe since the refractive index of the glycerol isequal to that of quartz. The light scattered by the sample is collectedby the objective lens and guided to the spectrometer. Silicon exhibits avery large absorption coefficient for the light of 364 nm, and the lightcan penetrate into Si by only about 10 nm. Therefore, an improvement canbe expected in the spatial resolution.

FIG. 9 illustrates Raman spectra of the Si substrate with (upper graph)and without (lower graph) the described probe contacting the (001) Sisurface. Without the probe, the peak at 520 cm⁻¹ is suppressed due tothe forbidden polarization configuration. With the metal-particle-toppedprobe in contact, however, the peak at 520 cm⁻¹ is enhanced because theselection rule is broken for the exciting light that is scattered at theend of the probe. Further, peaks from 800 to 1200 cm⁻¹ are stemming fromthe glycerol.

When the sample is a flat plate parallel of the (001) orientation of acrystal with the diamond or zinc blende structure, the invention can beimplemented by illuminating the sample in the [00-1] direction with thelight polarized in the [100] or [010] direction, and by detecting Ramansignal scattered in the [001] direction with the same polarization asthe incident light. For the same sample, further, the invention can beimplemented by the polarizing the incident light in the direction [110]or [1-10], and with the scattered light polarized perpendicular to theincident one, other conditions being equal. Further, the invention canbe implemented when the light is incident on the (110) plane andpolarized parallel to the [001] direction to prohibit the Ramanscattering polarized parallel to the same [001] direction.

EXAMPLE 6

Referring to FIG. 10, a sample forming a silicon belt of a width of 400nm and of a thickness of 100 nm on the (110) surface of an SOI substrateis studied by the Raman microscopy using an AFM probe carrying silverparticles of 50 nm diameter. The silicon belt is sandwiched by SiO₂ andis presumed to be distorted. It is expected that the Raman peak ofsilicon at 520 cm⁻¹ is shifted.

The exciting wavelength is 364 nm. The exciting light focused by theobjective lens has a spot diameter of about 1 um which is greater thanthe width of the belt. The arrangement for measurement is the same asthat of Example 5. FIG. 11 shows, as a function of center positions ofspots, the peak positions of Raman signals of when the center positionsof spots are scanned at an interval of 50 nm in a directionperpendicular to the silicon belt by using the probe and without usingthe probe. Without the probe, changes in the Raman shift are ratherweak. This is because, the beam spot diameter of the exciting light is 1μm which is greater than the width of the belt, and the spatialresolution is not sufficient. On the other hand, On the other hand, whenthe silver-particle-topped AFM probe is used, the Raman shift dependencebecomes more pronounced due to the improved spatial resolution.

EXAMPLE 7

In order to confirm the improvement in the spatial resolution of Ramanmeasurement by using a probe carrying silver particle, FIG. 12 shows asample obtained by etching holes of diameter of 100 nm in a siliconsubstrate and producing stress by thermal oxidation of the inner wallsof the holes. Raman measurement of the sample was taken with thesilver-particle-topped AFM probe (364 nm excitation) as well as with thesilver-coated probe (514.5 nm excitation). The results are as shown inthe following graph. When the probe is scanned on the sample surfaceaway from above the hole, the Raman shift changes from 520.7 cm⁻¹ to520.3 cm⁻¹. This reflects the fact that the oxidized holes induce thestress in the surrounding silicon, stress decreasing with the distancefrom the hole. The exciting light has a spot size of about 1 μm fromwhich it is concluded that the spatial resolution is improved by the useof the probe.

It will be further understood that when scanned by using the probecarrying silver particles, the peak position changes more sharply and abetter spatial resolution is obtained than when scanned by using theprobe coated with silver. This is due to that when the probe carryingsilver particles is used, the exciting light is scattered by the endportion only.

INDUSTRIAL APPLICABILITY

This invention can be extensively utilized as an optical measurementtechnology featuring a high resolution for evaluating properties of avariety of samples in such fields as nano-structures and nano-devicesthat have been studied and developed in recent years.

1. An optical measurement method including an optical arrangement formeasuring a signal light from a sample to be measured by irradiating thesample with exciting light, wherein: said optical arrangement is the onethat prohibits said signal light by a selection rule; and a probe isbrought close to said sample to be measured to locally relax theselection rule in only a portion near the end of said probe thereby toobtain the signal light.
 2. An optical arrangement method including anoptical arrangement for measuring a signal light from a sample to bemeasured by irradiating the sample with exciting light, wherein: saidoptical arrangement is the one that prohibits said signal light by aselection rule; and a probe having an end portion and other portionsmade of different materials at least on the surfaces thereof is broughtclose to said sample to be measured to measure the signal light.
 3. Anoptical measurement method according to claim 2, wherein said endportion has a material in the surface thereof different from the otherportions due to the surface treatment.
 4. An optical measurement methodaccording to claim 2, wherein said end portion is made of a materialdifferent from that of the other portions.
 5. An optical measurementmethod according to claim 2, wherein said probe uses, in the end portionthereof, a material having a large efficiency for scattering theexciting light and uses, in other portions thereof, a material having asmall efficiency for scattering the exciting light.
 6. An opticalmeasurement method according to claim 4, wherein said probe carries, onthe end portion thereof, fine particles of a material different fromthat of the other portions of the probe.
 7. An optical measurementmethod according to claim 6, wherein the other portions are made of amaterial transparent for the exciting light that is irradiated.
 8. Anoptical measurement method according to claim 6, wherein the otherportions are made of a glass or a plastic material.
 9. An opticalmeasurement method according to claim 6, wherein said fine particles arefine metal particles.
 10. An optical measurement method according toclaim 9, wherein said metal is any one of silver, gold, platinum orcopper.
 11. An optical measurement method according to claim 5, whereinsaid end portion and the vicinity thereof are immersed in a solutionhaving a refractive index close to a refractive index of a material ofthe other portions, and a measurement is taken by decreasing thescattering of the exciting light in the portions other than the endportion of the probe.
 12. An optical measurement method according toclaim 1, wherein said exciting light is ultraviolet light.
 13. Anoptical measurement method by causing exciting light to fall on acrystalline sample to be measured from a polarization direction in whichthe Raman scattering is prohibited by the selection rule, and bringing aprobe close to said sample to be measured to locally relax the selectionrule in only a portion near the end of the probe thereby to activate theRaman scattering and to detect Raman signals from only the portion nearthe end of the probe.
 14. An optical measurement method according toclaim 13, wherein said sample to be measured is a flat plate of a (001)orientation having a crystal structure which is a diamond structure or azinc blende structure, and scattered light of [100] polarization isdetected with the exciting light being polarized in the [100] direction.15. An optical measurement method according to claim 13, wherein saidsample to be measured is a flat plate of a (001) orientation having acrystal structure which is a diamond structure or a zinc blendestructure, the exciting light is incident on the sample in a direction[00-1] and is polarized in a direction [100] or [010], and signal lightscattered in a direction [001] which is the same polarization directionas the exciting light is detected.
 16. An optical measurement methodaccording to claim 13, wherein said sample to be measured is a flatplate of a (001) orientation having a crystal structure which is adiamond structure or a zinc blende structure, the exciting light isincident on the sample in a direction [00-1] and is polarized in adirection [110] or [1-10], and signal light scattered in a direction[001] which is a polarization direction at right angles with theexciting light is detected.
 17. An optical measurement method accordingto claim 13, wherein exciting light is caused to fall on a (001) planeof single crystalline silicon from a direction perpendicular to theplane such that the exciting light is polarized in the [110] directionand scattered light polarized in a direction at right angles therewithonly is detected, or exciting light polarized in parallel with the [001]direction is caused to fall on the (110) plane to prohibit the Ramanscattering polarized in parallel with the [001] direction.
 18. Anoptical measurement method according to claim 13, wherein said probe isscanned to measure a spatial distribution of Raman signals.
 19. Anoptical measurement method according to claim 3, wherein said probe isthe one coated with silver or gold.
 20. An optical measurement methodaccording to claim 1, wherein said sample to be measured is any one ofsilicon, diamond, germanium, Si—Ge mixed crystal, ZnS, ZnO, BN, BP, AlP,GaN, GaP, GaAs, InP, InAs, MSe (M=Be, Cd, Hg, Zn, Mn) or a mixed crystalthereof.
 21. An optical measurement device including an opticalarrangement for measuring a signal light from a sample to be measured byirradiating the sample with exciting light, comprising: means forlimiting the polarized state of the exciting light or the signal light;and means for bringing a probe close to the sample to be measured;wherein said probe is brought close to said sample to be measured tomeasure the signal light.
 22. An optical measurement device according toclaim 21, wherein said probe has an end portion and other portions madeof different materials at least on the surfaces thereof.
 23. An opticalmeasurement device according to claim 22, wherein said end portion has amaterial in the surface thereof different from the other portions due tothe surface treatment.
 24. An optical measurement device according toclaim 22, wherein said end portion is made of a material different fromthat of the other portions.
 25. An optical measurement device accordingto claim 24, wherein said probe uses, in said end portion thereof, amaterial having a large efficiency for scattering the exciting light anduses, in other portions thereof, a material having a small efficiencyfor scattering the exciting light.
 26. An optical measurement deviceaccording to claim 24, wherein said probe carries, on said end portionthereof, fine particles of a material different from that of the otherportions.
 27. An optical measurement device according to claim 24,wherein the other portions are made of a material transparent for theexciting light that is irradiated.
 28. An optical measurement deviceaccording to claim 24, wherein the other portions are made of a glass ora plastic material.
 29. An optical measurement device according to claim26, wherein said fine particles are fine metal particles.
 30. An opticalmeasurement device according to claim 29, wherein said metal is any oneof silver, gold, platinum or copper.
 31. An optical measurement deviceaccording to claim 21, wherein said end portion and the vicinity thereofare immersed in a solution having a refractive index close to arefractive index of a material of the other portions, and a measurementis taken by decreasing the scattering of the exciting light in theportions other than the end portion of the probe.
 32. An opticalmeasurement device according to claim 22, wherein said exciting light isultraviolet light.
 33. An optical measurement device according to claim21, wherein said sample to be measured is a flat plate of a (001)azimuth having a crystal structure which is a diamond structure or asphalerite structure, and scattered light of [100] polarization isdetected with the exciting light being polarized in the [100] direction.34. An optical measurement device according to claim 21, wherein saidsample to be measured is a flat plate of a (001) orientation having acrystal structure which is a diamond structure or a zinc blendestructure, the exciting light is incident on the sample in a direction[00-1] and is polarized in a direction [100] or [010], and signal lightscattered in a direction [001] which is the same polarization directionas the exciting light is detected.
 35. An optical measurement deviceaccording to claim 21, wherein said sample to be measured is a flatplate of a (001) orientation having a crystal structure which is adiamond structure or a sphalerite structure, the exciting light isincident on the sample in a direction [00-1] and is polarized in adirection [110] or [1-10], and signal light scattered in a direction[001] which is a polarization direction at right angles with theexciting light is detected.
 36. An optical measurement device accordingto claim 21, wherein said probe is scanned to measure a spatialdistribution of Raman signals.
 37. An optical measurement deviceaccording to claim 23, wherein said probe is the one coated with silveror gold.
 38. An optical measurement device according to claim 21,wherein said sample to be measured is any one of silicon, diamond,germanium, Si—Ge mixed crystal, ZnS, ZnO, BN, BP, AlP, GaN, GaP, GaAs,InP, InAs, MSe (M=Be, Cd, Hg, Zn, Mn) or a mixed crystal thereof.
 39. Anoptical measurement device according to claim 21, wherein provision ismade of: means for varying a distance between said probe and the surfaceof said sample to be measured; and means for taking a difference betweenthe intensity of signal light of when said probe is brought close to thesurface of said sample to be measured and the intensity of signal lightof when said probe is separated away therefrom.
 40. An opticalmeasurement device according to claim 21, wherein provision is made ofmeans for causing said exciting light to fall on the surface of saidsample to be measured nearly perpendicularly thereto and for detectingthe signal light from the surface of the sample nearly perpendicularlythereto.
 41. An optical measurement device according to claim 21,wherein provision is made of means for bringing said probe close to thesurface of said sample to be measured from a tilted direction.